The present invention generally relates to radiation sensors, and in particular, to temperature control and stabilization of radiation sensors.
2. Discussion of the Related Art
A radiation detector is a device that produces an output signal which is a function of an amount of radiation that is incident upon an active region of the radiation detector. Infrared detectors are radiation detectors that are sensitive to radiation in the infrared region of the electromagnetic spectrum. An infrared detector may be, for example, a thermal detector. A thermal detector detects radiation based upon a change in the temperature of an active region of the detector due to absorption of radiation incident to the detector.
Thermal imaging sensors may include a plurality of thermal detectors that detect a representation of an object by the objects"" thermal emissions. In particular, energy emitted by an object may depend on numerous quantities such as, for example, the emissitivity and the temperature of the object. Infrared thermal sensors typically detect one or both of these quantities and use the detected information to produce an object image that may be viewed, for example, on a display.
Infrared detectors may be classified as, for example, either cryogenic (typically liquid nitrogen temperatures) or uncooled detectors. Cryogenic infrared detectors are typically made of small band gap (about 0.1-0.2 eV) semiconductors such as HgCdTe, and operate as photodiodes or photo-capacitors by photon absorption to produce electron-hole pairs. In contrast, uncooled infrared detectors do not make use of the small band gap semiconductor device because the band gap is too small at, for example, room temperature, such that incident radiation would likely saturate the detector. Consequently, uncooled infrared detectors may be less sensitive than cryogenic detectors but do not necessarily require a cooling apparatus. Accordingly, for portable, low-power applications where the sensitivity of cryogenic detectors is not needed, an uncooled thermal detector is suitable. Examples of thermal detectors include pyroelectric detectors, thermocouples, and bolometers.
One example of a thermal imaging sensor is an array of bolometer detector devices. Such an array of bolometer devices may be monolithically formed on a semiconductor substrate together with an integrated circuit. The integrated circuit may be used to process electrical signals produced by the array of bolometers in response to the infrared energy incident to the array. In such an array, each of the bolometers includes an infrared energy receiving surface which is made of a material having a resistivity that changes as its temperature changes, in response to the infrared energy impinging on and being absorbed by the material. Thus, as the bolometer absorbs radiation, both its temperature and electrical resistance change. A measure of radiation absorbed by a bolometer can be made by measuring changes in its electrical resistance. For example, by placing the bolometer in series with a voltage supply, the current in the bolometer will vary in accordance with the amount of infrared energy incident to the bolometer. An electronic read-out circuit connected to the voltage supply and serially connected to the bolometer may be used to produce an output signal representative of the incident infrared energy. An array of such bolometers will produce a plurality of output electrical signals that may be fed to a processor and used to provide an electronic image of the source of the infrared energy.
For some applications, the signal response of such an array of bolometers, and other types of radiation sensors (e.g., thermal imaging sensors) in general, may benefit from various temperature control and/or stabilization techniques. Additionally, the signal response of such sensors may benefit from various compensation techniques which compensate the radiation sensor for potentially undesirable artifacts in the signals a due to, for example, changes in ambient temperature in the vicinity of the sensor.

One embodiment of the invention is directed to a method of controlling a temperature of at least one radiation sensor, wherein the radiation sensor outputs image signals based on detected radiation. The method comprises an act of varying the temperature of the at least one radiation sensor in response to a change in an ambient temperature proximate to the at least one radiation sensor.
Another embodiment of the invention is directed to a temperature sensitive reference circuit for providing a temperature sensitive reference signal in an apparatus including at least one radiation sensor to output image signals based on detected radiation. The temperature sensitive reference circuit comprises at least one temperature sensor to provide the temperature sensitive reference signal based on an ambient temperature proximate to the at least one radiation sensor, at least one power supply to provide power to the at least one temperature sensor, and at least one resistor coupled to the at least one temperature sensor and the at least one power supply.
Another embodiment of the invention is directed to a temperature control circuit for controlling a temperature of at least one radiation sensor that outputs image signals based on detected radiation. The temperature control circuit controls the temperature of the at least one radiation sensor based on a measured temperature of the at least one radiation sensor and a measured ambient temperature proximate to the at least one radiation sensor.
Another embodiment of the invention is directed to a method of compensating at least one radiation sensor for ambient temperature variations. The method comprises an act of controlling at least one of a radiation sensor bias voltage, a radiation sensor bias current, and a temperature of the at least one radiation sensor in response to changes in the ambient temperature.